It is well known that certain metals can experience far greater ductile deformation than expected in a single pass through a die if the metal to be reduced is maintained at a high hydrostatic pressure. A machine developed specifically to cold extrude metal or deform the metal under conditions of high hydrostatic stress is shown and described in U.S. Pat. No. 3,740,985, granted on June 26, 1973, to F. J. Fuchs. The machine disclosed in the Fuchs patent uses hydrodynamic friction to build the requisite pressure by surrounding the metal (to be extruded) with a pressure medium, some of which inevitably passes in minute quantities through the die along with the material being reduced.
The pressure media used (beeswax, polyethylene wax, etc.) are generally considered to be relatively solid at room temperature and atmospheric pressure. However, these media are sometimes referred to as Bingham solids, plastics, or fluids since they exhibit the measurable yield stress of a solid, and they plastically yield with the measurable viscosity of a liquid. They are thus workable as a viscous liquid at room temperature and high hydrostatic pressure when pressurizing the metal being extruded. This room-temperature pressure medium, as it leaves the die in minute quantities along with the wire, suddenly encounters atmospheric pressure and is in almost a solid state. The very high reaction force of the extrusion die is resisted by a tubular die stem, which is a hollow tube that extends from the die to the frame of the machine. The extruded wire passes through the central aperture of the die stem. The solidified pressure medium has a tendency to clog the central aperture of the die stem. This is particularly troublesome when beginning the reduction of a new batch of metal since the beginning of the reduced metal that is to be wound onto a reel encounters this solid pressure medium and is blocked thereby.